The present invention relates to fabricating elements or devices from a substrate having a size many times greater than that of a single element. More particularly, the present invention relates to tapered piezoelectric in-plane bimorphs and method of fabricating such bimorphs from a substrate of a size many times that of a single bimorph, wherein each bimorph has two angled opposing sides, a top having a top width, and a bottom having a bottom width which is greater than the top width.
As the areal density of concentric data tracks on magnetic discs continues to increase (that is, the size of data tracks and radial spacing between data tracks are decreasing), more precise head positioning is required. Head positioning in a hard disc includes two distinct but related aspects: tracking control (i.e., radial positioning of the head) and fly-height control (i.e., head-media spacing). Both aspects are important considerations for the hard discs in the future.
Conventionally, tracking control (radial head positioning) is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a head on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks.
One promising approach for high resolution tracking control involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby effecting head positioning through dual-stage actuation.
Conventionally, fly-height control is primarily accomplished using passive adjustments based on air bearing design. More recent disc drives, however, have started to use high resolution microactuation methods for actively controlling transducer head fly-height.
Various microactuator designs have been considered to accomplish high resolution head positioning. Some designs are employed to deform disc drive components such as the actuator arm or the flexure in order to achieve minute displacements by bending. Other designs introduce a separate microactuator component at an interface between disc drive components. U.S. Pat. No. 6,118,637 to Wright et al., for example, discloses an assembly including a gimbal, a piezoelectric element bonded to the gimbal and electrically connected to a voltage source, and a slider connected to the piezoelectric element. In the Wright patent, the microactuator (the piezoelectric element) is a separate unit that operates to change position of the entire slider.
The existing problems in the prior art schemes for a high resolution microactuator include difficulties in fabrication, large activation voltages required for deforming materials a sufficient amount to control the transducer position, lack of fast response bandwidth required in disc operation, and simplicity of implementation. To solve or alleviate these problems, careful considerations must be given to the type of the materials used to build the microactuator, internal structural designs of the microactuator, and location of the microactuator in the disc drive.
Among various microactuators used for high precision head positioning, piezoelectric microactuators are one of the most important. Among piezoelectric microactuators, piezoelectric bimorph microactuators are often used because they provide better performance than unimorph microactuators in many situations.
The piezoelectric bimorphs are well known in the industry. Such bimorphs are often used as transducers or microactuators. In general, a piezoelectric bimorph microactuator utilizes the opposite mechanical response of two pieces or regions of piezoelectric material to create a combined effect of bending. Depending on the bending direction, a piezoelectric bimorph microactuator can either be an out-plane type or in-plane type. A typical out-plane piezoelectric bimorph has two oppositely poled piezoelectric layers stacked and bonded together through a central electrode layer. As the two oppositely poled layers are activated such that one-layer expands and the other layer contracts, the bimorph will bend in a direction perpendicular to the direction of expansion and contraction (the length direction) because the two piezoelectric layers cannot move relative to each other.
In comparison, an in-plane piezoelectric bimorph microactuator has two opposing piezoelectric layers that are bonded side-by-side. As a result, the bimorph bends laterally in the planes of the piezoelectric layers instead of vertically when the two layers experience differential expansion (or contraction). It has been suggested that in-plane bimorph microactuators be used to effect a lateral microactuation in the disc drive.
U.S. application Ser. No. 09/876,463, filed Jun. 7, 2001, entitled “Combined Servo-Tracking and Preload-Controlling Microactuator”, describes a tapered piezoelectric in-plane bimorph microactuator located on the suspension loadbeam to bend the loadbeam. A tapered piezoelectric in-plane bimorph microactuator disclosed in that invention has two angled opposing sides, a top having a top width, and a bottom having a bottom width which is greater than the top width.
The tapered bimorph design helps to achieve a broader servo bandwidth (i.e., higher response frequency) and may be adapted to uses with many types of in-plane biomorph microactuators. The tapered design, however, also presents challenges in dicing operation during fabrication of the piezoelectric microactuators due to their two non-parallel sides.